It may have been raining cats and dogs outside, but things are looking bright for a Hamilton family who won $500,000 with Lotto First Division on Wednesday.

The winner, who wants to remain anonymous, bought his winning ticket on a whim when he emerged from the supermarket to find himself caught in a rainstorm.

"I'd just finished the grocery shopping and it started bucketing down. There was no way I wanted to go out in that, so I decided to grab a Lotto ticket while I waited for the rain to pass," said the winner.

"As the lady at the counter handed me the ticket I thought to myself, 'wouldn't it be a great story if this ended up being the winning ticket?' Then the rain stopped, so I headed to the car and thought nothing more of it."

It wasn't until Thursday that the winner remembered the lucky ticket he had tucked in his wallet.

"I checked the numbers and there they were, all in a line. I thought 'there's no way it can be that easy!' so I checked it again and again.

"When I was pretty sure I'd won, I called my wife over and said 'honey, we've won Lotto'," said the winner.

"And there was no way I believed him," laughed the winner's wife.

"So we ended up looking the results up on MyLotto and we saw that Countdown Dinsdale had sold the winning ticket - that's when she finally started to take me seriously," the winner said.

They couple then checked the ticket through the Lotto NZ App and started to get even more excited.

"I scanned the ticket with the app and all of a sudden 'major prize winner' popped up on the screen. That's when he really started jumping around," the winner's wife said.

With the winnings now safely in their bank account, the couple are looking forward to deciding what to do with their new-found fortune.

"We'll leave it in the bank for a bit while we work out what to do next. But whatever we decide, it's going to be really special," the winner said.

The winning ticket was sold at Countdown Dinsdale in Hamilton for the Lotto draw on Wednesday 19 April.